Heat exchanger device with heat-radiative coating

ABSTRACT

A heat retainer for a hot blast stove of a blast furnace, the heat retainer adapted to function without decomposition at temperatures of about 1200° C., wherein: at least one surface of said heat retainer is coated with a high radiative and highly-emissive material forming said coating layer; the thickness of said coating layer is critically between 0.02 mm and 3 mm; the heat retainer absorbs energy or emits energy mainly by radiation; and energy of radiation is mainly at a wavelength of 1-5 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 11/815,488 with a 371(c) date of Aug. 3, 2007, now pending, which is a National Phase Entry application under 35 U.S.C. 371 of International Patent Application No. PCT/CN2005/002010 with an international filing date of Nov. 25, 2005, designating the United States, now pending. This application further claims foreign priority benefits to Chinese Patent Application No. 200510043838.X, filed on Jun. 17, 2005. The contents of all of the aforementioned specifications as originally filed, and all amendment thereto, are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a heat exchanger device and more particularly to a heat storage device having a high radiative coating layer on the surface of the heat storage device, so that facilitates heat exchange.

2. Description of the Related Art

In industrial fields such as metallurgy, machinery and farm product processing, heat exchangers are commonly used. The main function of a heat exchanger is to transfer heat to air or gas. One type of heat exchangers uses coal, gas, oil or electricity as a direct heat source. Another type of heat exchangers employs secondary sources of heat. A heat source firstly transfers energy to a heat retainer of the heat exchanger, and then air or gas that needs to be heated is passed over it. During heat exchange between the heat retainer and the air or gas, heat is removed from the heat retainer, and the air or gas is heated. Generally, the heat retainer is made of a refractory material, a ceramic material, or a steel material.

Heat absorption and emission capability of heat retainers is an important factor for the heat exchange performance of a heat exchanger, and is directly associated with power savings. To improve the heat exchange efficiency of a heat exchanger, a plurality of patents, such as CN2462326Y and CN2313197Y, provide structural improvements of heat exchangers. However, a heat exchanger employing a coating layer made of high radiative material has not heretofore been proposed to improve the heat storage capability and working efficiency of the heat retainer.

SUMMARY OF THE INVENTION

To overcome the deficiencies of prior art, it is one objective of the invention to provide a highly-efficient and energy-saving heat exchanger with a coating layer on a part of or on the entire surface of the heat retainer for facilitating heat exchange.

In one aspect of the invention, provided is a heat exchanger with a coating layer for facilitating heat exchange, wherein at least one surface of the heat exchanger is coated with a coating layer.

In another aspect of the invention provided is a heat exchanger, comprising: a heat retainer and a coating layer, wherein the heat retainer is coated by the coating layer.

In certain embodiments of the invention, the matrix of the heat retainer is made of a refractory material, a ceramic material or a steel material.

In certain embodiments of the invention, the matrix of the heat retainer, i.e., the core, is made of a refractory material.

In certain embodiments of the invention, the matrix of the heat retainer, i.e., the core, is made of a ceramic material.

In certain embodiments of the invention, the coating layer made of a high radiative material.

In certain embodiments of the invention, the heat radiation of the coating layer is greater than the heat radiation of the core.

In certain embodiments of the invention, the heat emissivity of the coating layer is greater than the heat emissivity of the core.

In certain embodiments of the invention, the radiation of the high radiative material is greater than that of the substrate material of which the core of the heat retainer is made.

In certain embodiments of the invention, the high radiative material is a material having an absorption rate and an emission rate higher than those of the matrix material of which the core of the heat retainer is made.

In certain embodiments of the invention, the high radiative material is not highly-reflective.

In certain embodiments of the invention, the heat retainer is adapted for use in a high temperature heat exchanger.

In certain embodiments of the invention, the heat retainer is adapted for use in a hot blast stove of a blast furnace, or a coke battery.

In certain embodiments of the invention, the heat retainer is a heat retainer of a heat exchanger of a hot blast stove of a blast furnace, or a heat retainer of a heat exchanger of a coke battery.

In certain embodiments of the invention, the heat exchanger is adapted for use, and can be used without decomposition of the core and the coating layer, at temperatures exceeding 800° C., 825° C., 850° C., 875° C., 900° C., 925° C., 950° C., 975° C., 1000° C., 1025° C., 1050° C., 1075° C., 1100° C., 1125° C., 1150° C., 1175° C., 1200° C., 1225° C., 1250° C., 1275° C., 1300° C., 1325° C., 1350° C., 1375° C., 1400° C.

In certain embodiments of the invention the core and the coating layer will critically not decompose in a blast furnace during operation, where temperatures in the hot stove are below 1400° C.

In certain embodiments of the invention, the thickness of the coating layer is 0.02-3 mm.

In certain embodiments of the invention, the thickness of the high radiative material coating layer is critically not lower than 0.02 mm.

The thickness of the coating layer of between 0.02 and 3 mm is critical. The particular thickness of the coating has an unexpectedly beneficial effect on the adhesion between the coating and the matrix. When coatings of a smaller thickness than 0.02 mm or of greater thickness than 3 mm are used, the coating does not adhere well to the matrix.

In addition, only the particular thickness used and claimed allows the coating to properly infiltrate into the opening cavities of the core and allows for a permanent connection to form between the core and the coating.

The coating thickness combined with the shape of the retainer improves the basic mechanical properties and high temperature mechanical properties of the regenerator; it increases anti-corrosive properties with respect to high temperature flue gas; it protects the regenerator from slugging; and it prolongs the service lifetime of the regenerator compared.

In certain embodiments of the invention, the heat retainer takes the shape of a honeycomb, a fin, a rod, a brick, a ball, an ellipse or a plate.

In certain embodiments of the invention, the heat retainer is in the shape of a honeycomb.

In certain embodiments of the invention, the shape of the heat retainer is as shown in FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, or FIG. 7.

In certain embodiments of the invention, the shape of the heat retainer is substantially as shown in FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, or FIG. 7.

In certain embodiments of the invention, a cross section of the heat retainer is circular, square, rectangular, rhombic, hexagonal or polygonal.

In certain embodiments of the invention, the cross section of the heat retainer is in the shape of an elongated rectangle.

In certain embodiments of the invention, the cross sectional area of the core is square, rectangular, rhombic, hexagonal or polygonal.

In certain embodiments of the invention, the cross-sectional area of the core has a circumference, and the circumference comprises straight lines connected by non-straight lines.

In certain embodiments of the invention, the cross sectional area of the core is comprised of strips.

In certain embodiments of the invention, the heat retainer further comprises at least one cavity in the core.

In certain embodiments of the invention, a cavity passes through the matrix from its one end to another and the coating layer completely coats the surface of the cavity.

In certain embodiments of the invention, a plurality of inner holes is disposed within the heat retainer.

In certain embodiments of the invention, the inner holes are non-concentric with respect to one another.

In certain embodiments of the invention, the inner holes are fixed in space and immovable with respect to one another.

In certain embodiments of the invention, the cross sectional area of the cavity is square, rectangular, rhombic, hexagonal or polygonal, and the cross sectional area of the core is comprised of strips.

In certain embodiments of the invention, heat retainer is not a gauze.

In certain embodiments of the invention, the retainer is not in the shape of a gauze.

In certain embodiments of the invention, the inner holes are circular, square, rectangular, rhombic, hexagonal or polygonal.

In certain embodiments of the invention, the cross-sectional area of the inner holes is not very elongated.

In certain embodiments of the invention, when an external force is applied to the core, the individual cavities will not shift with respect to one another.

In certain embodiments of the invention, the high radiative material is any suitable high radiative far-infrared material suitable for a heat retainer made of a refractory material, a ceramic material or a steel material.

In certain embodiments of the invention, the coating layer comprises one or more of the following: Cr₂O₃, clay, montmorillonite, brown corundum, silicon carbide, TiO₂, Al₂O₃, Fe₂O₃, aluminum hydroxide, zirconium oxide, phosphoric acid, or hydrated sodium silicate gel.

In certain embodiments of the invention, the coating layer made of high radiative material is implemented by way of paste-coating, spray-coating or dip-coating, and the heat retainer having the coating layer is used directly after coating, or is used after high temperature curing.

In certain embodiments of the invention, surfaces of the substrate of the heat retainer are pre-treated with a pre-treating liquid prior to being paste-coated, spray-coated or dip-coated with the high radiative material, so as to further improve adhesion between the high radiative material and the substrate.

In certain embodiments of the invention, the pre-treating liquid is an aqueous solution containing polyamine curing agent PA80 (PA80 adhesive) or an alkali metal silicate and as a result the adhesion between the substrate and the high radiative material is increased.

In certain embodiments of the invention, the heat exchanger is prepared by coating surfaces of the substrate of the heat retainer with a pre-treating liquid and then paste-coating, spray-coating or dip-coated with the high radiative material to form a coating layer, wherein the pre-treating liquid is an aqueous solution of the polyamine curing agent PA80 or an alkali metal silicate.

The pre-treating liquid comprises one or more material that will not decompose in a blast furnace during operation, where temperatures in the hot stove are around 1200° C.

In certain embodiments of the invention, solid components in the high radiative material are hyperfinely processed, so as to enable the particle size to be between 20 and 900 nm, and to improve adhesion between the high radiative material and the substrate.

In certain embodiments of the invention, the core comprises a plurality of surfaces, the coating layer coats at least one the surface, the coating layer has been applied to at least one the surface by a process comprising: (a) coating at least one the surface with a pre-treating liquid; (b) paste-coating, spray-coating or dip-coating a high radiative material to form a coating layer; wherein the pre-treating liquid is an aqueous solution of a polyamine curing agent or an alkali metal silicate.

In certain embodiments of the invention, the core comprises a plurality of surfaces, the coating layer coats at least one the surface, the coating layer has been applied to at least one the surface by a process comprising: (a) pre-treating at least one the surface with a material increasing affinity of the core for the material to be applied in step (b); and (b) applying a material the heat emissivity of which is higher than that of the core to at least one the surface.

In certain embodiments of the invention, the coating layer increases the heat absorption and emission capability of the heat retainer, which improves heat absorption and emission of the heat retainer, and increases the heat storage capacity.

In certain embodiments of the invention, the coating layer increases the radiation efficiency of the retainer compared to what the radiation efficiency would have been if no coating layer were used.

In certain embodiments of the invention, the coating layer achieves savings of over 20% of energy compared to what the energy usage would have been if no coating layer were used.

In certain embodiments of the invention, the coating layer achieves rapid and efficient heat transfer and increases the heat storage capacity of the heat retainer.

In certain embodiments of the invention, the heat retainer is adapted to transfer heat mainly by radiation.

In certain embodiments of the invention, the heat retainer is adapted to transfer more heat by radiation than by convection.

In certain embodiments of the invention, the heat retainer is adapted to absorb and emit heat non-simultaneously.

In certain embodiments of the invention, the coating layer increases heat absorption and heat radiation ability of the core.

In certain embodiments of the invention, the heat exchanger is adapted to receive heat by gasses flowing through the inner holes.

In certain embodiments of the invention, the coating acts to increase the radiative ability of the matrix.

In certain embodiments of the invention, the heat retainer with a high radiative coating decreases the high-temperature creep rate by about 40% compared with that of conventional heat retainers.

In certain embodiments of the invention, the heat storage ability of the heat retainer with a high radiative coating is unexpectedly higher by at least about 15% at under 1300° C. compared with that of conventional heat retainers art.

In certain embodiments of the invention, the heat retainer with a high radiative coating improves the regenerator's heat absorption ability during combustion period and heat emission ability during blast period in blast furnace hot stoves.

In certain embodiments of the invention, the working efficiency and thermal efficiency of blast furnace hot stoves are increased.

In certain embodiments of the invention, the hot blast temperature is increased by at least 15° C., the exhaust gas temperature is reduced by at least 13° C., and gas consumption is decreased by at least 7%. In addition, the reduction of CO₂ emission is successfully realized. Besides, the high radiative coating can prolong the blast time by at least 10%, and/or decrease the flue gas temperature by more than 10%.

When high radiative material is used on the surface of regenerators, heat storage and heat emission of the heat exchanger made of the heat retainer do not occur simultaneously. Particularly, heat storage occurs during a heat storage period, and the high radiative material improves the ability of the matrix to absorb heat. Then, heat radiation and emission takes place during heat emission period, and the high radiative material improves the ability of the matrix to release heat. For example, for hot stoves of blast furnace used for iron-making, the heat storage period of a heat retainer according to this invention is generally 110 min and the heat emission period is about 55 min, and the blast furnace hot stoves go through the two periods alternately.

Coating a heat retainer with a high radiative material achieves the goal of absorbing more heat during heat storage period as compared with uncoated retainers by increasing the thermal radiative absorption rate of the surface of the matrix, and releasing more heat during heat emission period as compared with uncoated retainers by increasing the thermal radiative emission rate of the surface of the matrix. The end temperature of the matrix is comparatively increased during heat storage period and the end temperature of the matrix is comparatively decreased during heat release period.

Most energy radiated at high temperature concentrates in the wavelength region of between 1 and 5 micron. When a heat retainer is coated with high radiative coating, the coating inherently allows heat to be absorbed and later released by radiation at a wavelength in 1 to 5 micron. (High radiative coating has high radiativity within 1 to 5 micron wavelength range.) Energy at that wavelength is more easily absorbed by the heated bodies.

In certain embodiments of the invention, the coating of high radiative material increases the heat exchange efficiency of the heat retainer and saves energy. Particularly, when a checker brick of a hot blast stove of a blast furnace is coated with the high radiative material, temperature inside the hot blast stove is uniformly distributed, and the heat storage capacity is notably increased.

In certain embodiments of the invention, when the heat retainer is placed in a hot blast stove of a blast furnace at their normal operating temperature, the heat retainer will absorb heat from hot air mainly by thermal radiation.

In certain embodiments of the invention, the heat retainer is a checker brick, or a similar type.

In another aspect of the invention provided is a method for improving the efficiency of heat transfer in a heat retainer for a heat exchanger, comprising coating a surface of the heat retainer with a high radiative material.

In another aspect of the invention provided is a method for improving the efficiency of heat transfer in a heat retainer for a heat exchanger, comprising using a heat retainer coated with a high radiative material to absorb heat during a heat absorption period and later emit heat during a heat radiation period.

In certain embodiments of the invention, steady state for heat exchange is not achieved during the heat absorption period and/or during the heat radiation period.

In another aspect of the invention provided is a method for enhancing radiative heat absorption and radiative heat emission and for simultaneously reducing heat reflection in a heat retainer for a hot blast stove of a blast furnace, comprising: placing into a hot blast stove of a blast furnace a regenerator coated with a coating layer, and operating the hot blast stove of the blast furnace at usual operating temperatures described above.

In certain embodiments of the invention, when the heat retainer absorbs heat from hot air in a hot blast stove of a blast furnace, the temperature of the heat retainer increases substantially.

In certain embodiments of the invention, the method further comprises placing the heat retainer into a hot blast stove of a blast furnace.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described hereinbelow with reference to accompanying drawings, in which:

FIG. 1 shows a honeycomb-shaped heat retainer with a coating layer according to one embodiment of the invention;

FIG. 2 shows a honeycomb-shaped heat retainer with a coating layer according to another embodiment of the invention;

FIG. 3 shows a fin-shaped heat retainer with a coating layer according to another embodiment of the invention;

FIG. 4 is a partial cross-sectional view illustrating a plate-shaped heat retainer with a coating layer according to yet another embodiment of the invention;

FIG. 5 is a partial cross-sectional view illustrating a ball-shaped heat retainer with a coating layer according to yet another embodiment of the invention;

FIG. 6 shows an elliptical heat retainer with a coating layer according to yet another embodiment of the invention;

FIG. 7 is a partial cross-sectional view illustrating a non-metallic heat retainer with a coating layer according to yet another embodiment of the invention;

FIG. 8 shows temperature profile during a heat absorption period (temperature rising) and heat emission period (temperature falling) of a heat retainer with a coating layer according to the invention as compared to a similar uncoated retainer;

FIG. 9 shows a heat retainer in the shape of a rod with a coating layer according to another embodiment of the invention;

FIG. 10 shows physical model of checker brick passage in a regenerator according to one embodiment of the invention;

FIG. 11 shows the temperature difference between flue gas and bricks along top-to-down direction for hot stoves with coatings or without coatings at 110 minutes in the combustion period according to one embodiment of the invention;

FIG. 12 shows temperature difference between checker brick and blast during blast period along top-to-down direction for hot stoves with coatings or without coatings according to one embodiment of the invention;

FIG. 13 a shows changing curves of the blast temperature with respect to the calculation results and test results for the 3^(#) hot stove without coating, and FIG. 13 b shows changing curves of the blast temperature with respect to the calculation results and test results for the 1^(#) hot stove with coating according to one embodiment of the invention; and

FIG. 14 a shows changing curves of the temperature of flue gas with respect to the calculation results and test results for the 3^(#) hot stove without coating, and FIG. 14 b shows changing curves of the temperature of flue gas with respect to the calculation results and test results for the 1^(#) hot stove with coating according to one embodiment of the invention.

Reference list: 1—circular inner hole; 2—high radiative material coating layer; 3—circular inner hole; 4—high radiative material coating layer; 5—rectangular inner hole; 6—highly-radiative material coating layer; 7—high radiative material coating layer; 8—substrate; 9—heat exchange surface; 10—substrate; 11—high radiative material coating layer; 12—heat exchange surface; 13—substrate; 14—high radiative material coating layer; 15—heat exchange surface.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in Table 4 below, the radiative rate of common refractory materials commonly used to make heat retainers is between about 0.6 and about 0.8 at room temperature. However, the radiative rate decreases significantly when the temperature increases. In a hot stove of a blast furnace during operation, where temperatures in the hot stove are around 1200° C., the radiative rate of common regenerative materials is only between about 0.4 and 0.5. Thus, the heat exchange efficiency is low. Much heat is lost with exhaust gases instead of being absorbed by the regenerative materials. To improve efficiency of the heat retainers, the radiative rate of the new high radiative rate coating is above about 0.9 at around 1200° C.

In addition, generally, when the temperature is over 900° C., heat radiation becomes the principal mode in heat transfer process (with over 90% of heat being transferred by radiation). Energy radiated at high temperature concentrates in the wavelength region of between 1 and 5 microns. When a heat retainer is coated with high radiative coating, the coating inherently allows heat to be absorbed and later released by radiation at a wavelength in 1 to 5 micron. (High radiative coating has high radiativity within 1 to 5 microns wavelength range.) Energy at that wavelength is more easily absorbed by the heated bodies. Therefore, a coating of a high radiative material disposed on a heat retainer effectively increases the capability of heat absorption and heat emission, and increases the heat exchange efficiency of the heat retainer at high temperatures. Beyond this, the coating layer also increases the heat absorption and heat radiation ability of the core of the heat retainer.

The heat retainer experiences the heat storage period and heat release period alternately in industrial application, and the heat retainer absorbs and emits heat non-simultaneously. In the heat storage period, the heat retainer absorbs energy which is usually generated by combustion of fuel; in the heat release period, the heat retainer emits energy to the blast which is used as air for circulation. The end temperature of the regenerator is comparatively increased during heat storage period and the end temperature of the regenerator is comparatively decreased during heat release period relative to heat retainers not coated with the coating described herein.

The heat retainer coating made of a high radiative material absorbs more heat during heat storage period as compared with an uncoated retainer by increasing the thermal radiative absorption rate of the surface of the matrix, and has higher radiation rate of the surface matrix during heat emission period as compared with uncoated retainers by increasing the thermal radiative emission rate of the surface of the matrix. Thus, the end temperature of the matrix is comparatively increased during heat storage period and the end temperature of the matrix is comparatively decreased during heat release period.

In addition, the working efficiency and thermal efficiency of the heat exchangers coating with a high radiative material are increased as compared with uncoated heat exchangers. This raises the temperature of hot blast, shortens the heat storage period, prolongs the heat release period, and reduces the gas consumption and air flow. Reduction of the gas consumption and the air flow further saves energy, reduces coke consumption and, correspondingly, reduces CO₂ emissions.

In addition, the nano/micro coating materials filled the cavity on the surface of the heat retainer which protects the heat retainer and increases its service life. The coating layer of the heat retainer also operates to protect the substrate of which the core of the heat retainer is made. The following features of the heat retainer are improved after coating with a high radiative material: the volume density, the crushing strength, tensile strength and the softening temperature with loading. However, the pore rate and the distortion rate of the heat retainer are decreased after coating which are good for prolonging the service life of the heat retainer.

In addition, when the surfaces of the regenerator of a steel-rolling regenerative furnace are coated with the high radiative material, temperature of the core of the heat retainer increases significantly. The thickness of the coating layer allows the coating to infiltrate into the opening cavities of the core and allows for a permanent connection to form between the core and the coating. The coating having critically the particular thickness combined with the shape of the retainer increases the basic mechanical properties and high temperature mechanical properties of the heat retainer, increases anti-corrosive properties with respect to high temperature flue gas, protects the heat retainer from slugging, and prolongs the service lifetime of the heat retainer.

The high radiative material forming a coating layer on the heat retainer may be freely selected. The below embodiments are intended to be illustrative only, and are not meant to limit the invention.

Example 1

As shown in FIG. 1, a heat retainer used for a hot blast stove of a blast furnace is a checker brick. The checker brick (heat retainer) has a plurality of circular inner holes 1, and all surfaces (comprising those of the inner holes) of the check brick (heat retainer) are coated with a coating layer of a high radiative material 2 whose thickness is 0.02 mm. A substrate of the heat retainer is a refractory material, and the high radiative material coating layer 2 is a high radiative material whose emissivity in the far-infrared region is greater than that of a substrate material of the heat retainer.

The high radiative material coating layer 2 comprises by weight: 110 parts of Cr₂O₃, 80 parts of clays, 90 parts of montmorillonites, 300 parts of brown corundum, 100 parts of silicon carbides, 400 parts of PA80 adhesive and 100 parts of water. These components are hyperfinely processed, i.e., the mixture is grinded to particles with micro/nano-meter sizes by using superfine processing technique, so as to enable the particle size to be in the 25-700 nm range. Compared with existent heat exchangers, the heat exchanger of this example saves over 20% of energy.

Example 2

As described in example 1, except that differences are as follows: the cross section of the honeycomb-shaped heat retainer is rectangular; and the high radiative material coating layer is disposed within a plurality of circular inner holes 3 (as shown in FIG. 2).

Example 3

As shown in FIG. 3, the heat retainer for a heat exchange is fin-shaped. A plurality of rectangular inner holes 5 are disposed in the heat retainer, and all surfaces (comprising surfaces of the inner holes) of the heat retainer for the heat exchanger are paste-coated with a high radiative material coating layer 6 whose thickness is 0.03 mm. A substrate of the heat retainer is a ceramic material, and the high radiative material coating layer 4 is a high radiative material whose emissivity in the far-infrared region is greater than that of a substrate material of the heat retainer.

The high radiative material comprises by weight: 15 parts of zirconium oxide, 8 parts of Cr₂O₃, 10 parts of TiO₂, 2 parts of montmorillonites, 15 parts of Al₂O₃, 10 parts of carborundums, 30 parts of PA80 adhesives, and 10 parts of water. Compared with existent heat exchangers, the heat efficiency of the heat exchanger according to this example is improved by over 10%.

Example 4

As shown in FIG. 4, the heat retainer for use in a heat exchanger according to this example is plate-shaped; and the surfaces of the heat retainer are paste-coated with a coating layer 7 made of a high radiative material and whose thickness is 0.1 mm. A substrate 8 of the heat retainer is a steel material, and the high radiative material is a high radiative material whose emissivity in the far-infrared region is greater than that of the substrate material.

The high radiative material comprises by weight: 60 parts of Cr₂O₃, 200 parts of brown corundums, 50 parts of clays, 30 parts of montmorillonites, 200 parts of silicon carbides, 200 parts of hydrated sodium silicate gels, and 100 parts of water. The outer surface of the coating layer 7 is the heat exchange surface 9. The surfaces of the heat retainer are coated with a pre-treating liquid prior to being paste-coated with the high radiative material. The pre-treating liquid comprises 10% aqueous solution (by weight) of PA80 adhesive. Compared with existent heat exchangers, the heating efficiency of the heat exchanger of this example is improved by over 10%.

Example 5

As shown in FIG. 5, the heat retainer for a heat exchanger is ball-shaped, and the surfaces of the heat retainer are paste-coated with a high radiative material resulting in a coating layer 11 whose thickness is 0.3 mm. An outer surface of the coating layer 7 is the infiltrating layer 12 whose thickness is 2 mm. A substrate 10 of the heat retainer is a refractory material, and the high radiative material forming the coating layer 11 is a high radiative material whose far-infrared emissivity is greater than that of a substrate material.

The high radiative material comprises by weight: 5 parts of zirconium oxide, 10 parts of silicon carbides, 5 parts of titanium, 3 parts of clays, 40 parts of brown corundums, 10 parts of aluminum hydroxides, 15 parts of phosphoric acid, and 12 parts of water. Compared with existent heat exchangers, the relative temperature of the heat exchanger of this example is increased by over 15° C. The heat retainer according to this example is applicable for use as a regenerative furnace, in which the ball-shaped heat retainer exchanges heat within a heat accumulator being part of the regenerative furnace.

Example 6

As described in example 5, with the change that the heat retainer for a heat exchanger is elliptical in shape (as shown in FIG. 6).

Example 7

The surfaces of a ball-shaped heat retainer are spray-coated with a high radiative material giving rise to a coating layer whose thickness is 2.5 mm.

The coating layer comprises by weight: 15 parts of silicon carbide, 2 parts of brown corundum, 35 parts of zirconia, 2 parts of montmorillonite, 6 parts of chromium oxides, 27 parts of PA80 adhesives and parts of 13 water.

The surfaces of the heat retainer are coated with pre-treating liquid prior to being spray-coated with the high radiative material, the pre-treating liquid comprising a 10% by weight aqueous solution of hydrated sodium silicate gels.

Example 8

As shown in FIG. 7, the surfaces of a ceramic substrate 13 of a heat retainer are paste-coated with a high radiative material resulting in a coating layer 14 whose thickness is 3 mm. The outer surface of the coating layer 14 is the heat exchange surface 15.

The coating layer comprises by weight: 60 parts of Fe₂O₃, 5 parts of zirconia, 20 parts of hydrated potassium silicate gels and 15 parts of water. The surfaces of the heat retainer are coated with a pre-treating liquid prior to being paste-coated with the high radiative material coating layer. The pre-treating liquid comprises 8% aqueous solution (by weight) of PA80 adhesive.

Example 9

A checker brick is coated with a high radiative material. The material is mainly made from sintering agent, suspending agent and adhesives, etc. First, the solid component is weighed according to the designed composition. The mixture to micro/nano-size is then grinded using superfine processing technology. The micro/nano powder are mixed with adhesives and a thermoplastic polymer and a small number of surfactant are added. Finally, high-speed mechanical agitation is used to form the high radiative coating product into a viscous fluid.

The coating is applied by the following processes: cleaning dust for the checker brick→spraying adhesives→coating by soaking→drying.

The coated checker brick is heated in the furnace to 1100° C. and water quenched repeatedly. The coating layer adheres well as a result and there are no cracks or shedding after the coating process is completed.

Specifically, when the bricks were broken to expose the interface of the core and the coating layer:

-   -   the coating did not shed;     -   the interface between the coating and the brick had no cracks,         which shows shat the coating and the brick can be closely         integrated together;     -   the small coating particles infiltrating into the matrix existed         in the cracks of the bricks;     -   the coating infiltrated into brick well, and     -   the composition of the brick did not react chemically with other         substances or generated a low melting phase.

Example 10

Heat-absorption and heat-release rates of high-alumina and silica checker bricks were conducted respectively under the same conditions. The two specimens having the same volume were prepared from the same checker brick. One of the specimens was coated with the coating, whereas the other one was not.

Both the heating speed and the cooling speed of the bricks with coating were faster than that of the uncoated specimen during the heating and cooling period. The specimen with coating has a higher capacity of heat regenerative than that of the uncoated one.

The heating and cooling curves of the specimens are shown in FIG. 8. It can be clear seen that the temperature of the specimen with coating is higher than that of the uncoated one during the heating process, and the maximum temperature difference reached 283° C., 13 minutes after the start of heating. The coated specimen reached 1142° C., whereas the uncoated specimen reached only 1067° C.

The result shows that the coated specimen with higher heat absorption capability can reach the designed temperature in a shorter time. Thus, the coating is superior for heat absorption during combustion period in hot stove and results in reducing the heating time in the BF hot stove. In addition, the initial temperature at the beginning of the heat emission period of the coated specimen is 1142° C. and that of the uncoated one is 1067° C. Also, the cooling time from the initial temperature to 390° C. for the coated specimen was 6 minutes and that for the uncoated one was 11 minutes. Thus, the coating is also superior for heat emission during blast period in hot stove and result in reducing the blast time.

Properties of the corresponding coated and uncoated checker bricks are summarized in Tables 1-3.

TABLE 1 Performance comparison between coated and uncoated high-alumina checker brick Strength of Volume Pore compression Break Distortion density rate resistance strength rate (g/cm³) (%) (MPa) (MPa) (%) Without coating 2.43 25 49 5.8 −1.424 With coating 2.48 21 64 6.3 −0.623

TABLE 2 High temperature physical properties contrast between uncoated and coated silica bricks (1300° C. × 3 h) Strength of Volumn compression Break density Pore rate resistance strength Distortion rate (g/cm³) (%) (MPa) (MPa) (%) Without 1.80 19.88 28 12.23 +0.51 coating With coating 1.81 19.27 31 12.65 +0.33

TABLE 3 Softening temperature with loading and the distortion rate contrast between uncoated and coated silica bricks Softening temperature High temperature with loading distortion rate (0.2 MPa, 0.6%), ° C. (1430° C. × 50 h), % Without 1550 +0.405 coating With coating >1650 −0.074

As shown in Tables 1-3, the following features of the heat retainer are improved after coating with a high radiative material: the volume density, the crushing strength, tensile strength and the softening temperature with loading. In addition, the pore rate and the distortion rate of the heat retainer are decreased after coating which is superior for prolonging the service life of the heat retainer.

The nano/micro-size particles of the coating material filled the cavity on the brick surface, which decreases the pore rate and increases the volume density. This is superior for increasing the strength of compression resistance and anti-corrosive properties with respect to high temperature flue gas, decreasing the distortion rate of the brick, and protecting the regenerator from slugging. All of these improvements help to prolong the service life of the blast furnace hot stove.

Example 11

Take the “Jie Neng Wang” Nano/Micro-Meter High-Temperature Infrared Energy-Saving Coating (HM-HRC)'s application in Shandong Shiheng Steel Company as an example, where there is a 1080 m³ BF with 3 hot stoves. The 34 layers of siliceous checker bricks on the top of the high temperature region of the 1^(#) and 2^(#) hot stoves are coated with HM-HRC invented and produced by Shandong Huimin Science & Technology Co., Ltd., while the 3^(#) hot stove is without coating.

We analyzed the hot air flow and heat transfer process inside hot stoves with and without HM-HRC, respectively. It is well known that during the combustion period, the radiative and convective heat transfers between the high-temperature flue gas and checker bricks are the principal heat transfer modes, and the heat conduction also exists inside the check bricks simultaneously. During the blast period, the cool air is heated when it passes through the checker bricks, and the checker bricks are cooled down at the same time.

Along the altitude-direction, the temperature of checker brick surface is very high, the maximum can reach up to more than 1300° C. and the bottom is about 300° C. (the height of regenerator chamber was 31.7 m.). In order to simplify the calculation, the regenerator chamber was divided into three different zones from top to bottom. The mathematical model of the radiation and convection heat transfer inside the regenerator chamber have been set up according to the energy balance between the flue gas and the regenerator as well as heat conduction of regenerator.

Using the CFD software, we simulated the heat transfer process inside regenerator chamber; made a quantitative analysis and comparison of hot blast temperature, flue gas temperature and checker bricks' surface temperature of 1^(#) hot stove (with HM-HRC) with those of 3^(#) hot stove (without HM-HRC), then got the radiation rate influence on the hot blast temperature and the flue gas temperature. At last, we made a comparison of the numerical results with detected results in 1^(#) and 3^(#) stoves.

Physical Model of the Hot Blast Stove

Analysis of Fluid Flow Heat Transfer Inside Regenerator Chamber

During the combustion period, high temperature flue gas heats the checker bricks in the stove from top to bottom. During blast period, the cold air flows through the checker brick from bottom to top and turns into hot blast by absorbing heat from regenerators, and finally is delivered to blast furnace.

The Technology Parameters of Hot Blast Stove

The Characteristic of Hot Blast Stove

The calculation model is based on the following parameters: number of hot blast stove is 3; height of regenerator chamber is 31.7 m; cross-section area of regenerator chamber is 35.8 m²; regenerator chamber is divided into 3 regions; surface area of hot stove body is 781 m²; surface area of hot air pipe is 325 m². The checker brick has 19 holes and the inner diameter of holes is 31 mm. The bricks from top to bottom in hot stoves are: silica brick, 9.6 m; high alumina brick, 7.8 m; ordinary density clay brick, 14.3 m.

Operation Parameters of the Hot Blast Stove

The operational rule for hot blast stove is “two in combustion, one in blast”. The combustion cycle is 114 min, the blast cycle is 55 min, stove cutover takes 10 min.

During the test period, the combustion air temperature of hot blast stoves is 183° C.; the cool air inlet temperature of both 1^(#) and 3^(#) stoves is 171° C.; the average hot blast temperature of 1^(#) is 1198° C. and 3^(#) is 1173° C., the average flue gas outlet temperature of 1^(#) and 3^(#) is 300° C. and 313° C., respectively.

The dry gas component of hot stove is measured on site by flue gas analysis meter. After the beginning of test period, the analysis result is recorded every 15 minutes. Then the average result is calculated and conversed into humid components according to experiential formula.

Thermal Physical Performance of Checker Brick in Regenerator of Hot Stove

Specific Heat and the Heat Conduction Coefficient of Checker Brick

The thermal physical characteristic of checker brick is a linear function of temperature, i.e., a+b t. In this project, the checker bricks in the three different parts have different physical performance function coefficient a and b, as shown in Table 4.

TABLE 4 Thermal physical characteristics of checker bricks Coefficient of heat Specific heat conductivity a b a b Silica brick 0.19  0.7 × 10⁻⁴ 0.93   0.197 × 10⁻³ Andalusite high- 0.20 0.56 × 10⁻⁴ 1.52  −0.19 × 10⁻³ alumina brick Clay brick 0.20 0.63 × 10⁻⁴ 0.836    0.58 × 10⁻³

Surface Radiativity of Checker Brick

As is known from references^([1]), the radiation rate of firebricks is usually 0.6˜0.8 under room temperature; meanwhile, with stoves' temperature increasing, the radiation rate decreases dramatically. When temperature rises to 800° C.˜1000° C., the blackness is 0.5; when temperature rises to 1300° C., the blackness drops to 0.4. However, the radiation rate of Nano/Micro-Meter High Temperature Infrared Energy Saving Coating is always over 0.9 from room temperature to high temperature.

Mathematical Model

Simulation Object

The simulation object is regenerator chamber. According to the fluid flow features of flue gas inside the holes of checker bricks during the combustion and the blast period, the heat transfer process of regenerator chamber is simplified into a cluster of flow pipes, assuming that the flux speed and temperature distribution into every checker brick hole are the same during the numerical simulation calculation, as shown in FIG. 10. The inner diameter of flow pipes is the diameter of the holes. The outer diameter of bricks is:

$d_{0} = {2 \times {\sqrt{\frac{A_{s}}{\pi \; N_{s}}}.}}$

Where A_(s) is upper surface area of one brick with 19 holes (including area of holes). Ns is number of the holes.

Radiative Heat Exchange Model

The radiative quantity of heat exchange is proportional to the fourth power of temperature under high temperature; radiative heat transfer is the principal way of heat transfer. The quantity of heat exchanged by radiation is: Q_(rad)=σ(T_(max) ⁴−T_(min) ⁴). As for the medium with absorption, emission and dispersion characteristic, the radiative transmission equation on position {right arrow over (r)}, along direction {right arrow over (s)} is:

${\frac{{I\left( {\overset{\rightarrow}{r},\overset{\rightarrow}{s}} \right)}}{s} + {\left( {a + \sigma_{s}} \right){I\left( {\overset{\rightarrow}{r},\overset{\rightarrow}{s}} \right)}}} = {{{an}^{2}\frac{\sigma \; T^{4}}{\pi}} + {\frac{\sigma_{s}}{4\pi}{\int_{0}^{4\pi}{{I\left( {\overset{\rightarrow}{r},{\overset{\rightarrow}{s}}^{\prime}} \right)}{\Phi \left( {\overset{\rightarrow}{s},{\overset{\rightarrow}{s}}^{\prime}} \right)}\ {\Omega^{\prime}}}}}}$

Numerical Simulation Result and Analysis

The equation is solved by CFD equation solver, the flue gas temperature and checker brick surface temperature changes during combustion period, and the blast temperature and checker brick surface temperature changes during air heating period of 3^(#) stove and 1^(#) stove are obtained, their change regularities are summarized as following.

Temperature Difference Between Flue Gas and Checker Brick During Combustion Period

FIG. 11 illustrates the temperature difference between flue gas and bricks along top-to-down direction and the comparison between hot stoves with coatings and without coatings at 110 minutes in combustion period. The temperature difference in the top is larger than that at the bottom of regenerator chamber; because of heat exchanges between the flue gas and checker bricks, the flue gas temperature gradually lowers and the temperature difference gradually decreases. The temperature difference is the lowest at the flue gas outlet.

From the comparison between regenerator chambers with and without HM-HRC, the temperature difference decreases after 34-layer silica bricks on the top of regenerator chamber in hot stoves which are coated with high radiative coating, and this indicates that the heat absorption of checker bricks was speeded up during combustion period, so heat absorption capacity increases; meanwhile, the thermal storage capacity of checker bricks increases. Although only 34 layers of checker brick in the upper region of regenerator chamber is coated, it has affected the heat transfer of the whole regenerator chamber; especially the top 80% region of regenerator chamber, the effect is more conspicuous.

Temperature difference between checker brick and blast during blast period.

From FIG. 12, it can be seen that during 55 minutes of blast period: the temperature differences between checker brick and blast are almost the same. Higher checker brick temperature means higher blast temperature. Since the heat absorption capacity and temperature of checker brick with coating are higher during combustion period, the temperature difference between the checker bricks and blast with coating is the same or less than that without coating, which indicates that the checker brick with coating has stronger heat radiativity, the heat capacity is more than that without coating, so the blast temperature is increased.

Comparison Between Calculation Results and Test Results on Site

Temperature of Blast Outlet

FIG. 13 a and FIG. 13 b show the blast temperature changed with time during the blast period for the 3^(#) hot stove without coating and 1^(#) hot stove with coating. The dashed line is the numerical simulation result, and the red line is the detected data curve on site separately. By comparing the curves for the two hot stoves, we can see that the blast temperature of 1^(#) hot stove is higher than that of 3^(#) hot stove.

The Outlet Temperature of Flue Gas

FIG. 14 a describes the temperature of exhaust gas from 3^(#) hot stove without coatings. The highest temperature is about 400° C., the lowest temperature is 198° C. or so, the average temperature is about 313° C. FIG. 14 b describes the temperature of flue gas from 1^(#) hot stove with coatings. The highest temperature does not reduce much, but the average temperature reduces 13° C. than 3^(#) hot stove. The calculated results are lower than the actual data, but the error is within the tolerance of 10%.

If thermal losses of stove walls and heterogeneity of regenerator materials are taken into account, the calculated results would be smaller and be closer to the actual values.

Conclusions

The numerical calculation results confirm: 1. During combustion period, in the top region of regenerator chamber, the temperature difference of checker bricks with coating is smaller than that without coating, the heat absorption speed and the heat storage capacity of checker bricks in the whole regenerator chamber is increased. 2. During blast period, the temperature differences between checker brick and blast in hot stoves with coating and without coating are almost the same. Since the regenerator with coating has stronger heat storage capacity and higher temperature, the fact that the temperature differences between checker brick and blast are the same indicates that the hot blast temperature of hot stove with coating is higher. 3. The average blast outlet temperature with coating increases more than 20° C. and the flue gas outlet temperature decreases more than 10° C., which are similar to the detected results on site.

Example 12

In order to measure the heat-using condition and thermal efficiency changing after using the high radiative coating on the checker bricks of BF hot blast stove, to evaluate the thermal characters and to have a deeper understanding of the principle—the high radiative coating improves thermal efficiency, Shandong Huimin Science & Technology Co., Ltd., University of Science & Technology Beijing, Shandong Shiheng Steel Co., Ltd., Shandong province Energy Detection Center and other units carried out the energy-saving thermal diagnostic testing and thermal process diagnosis and comparison on Shiheng steel company 1080 m³ BF 1^(#) and 3^(#) hot blast stoves, and also made a diagnosis of heat flow and heat distribution of 3^(#) hot blast stove (without coating) and 1^(#) hot blast stove(with coating). According to the results, of the hot blast stove (with the high radiative coating), the blast temperature improved, exhaust air temperature decreased, and thermal efficiency improved by 5%.

Introduction

In the industrial furnace, heat transfer mainly by way of radiation. Considering the industrial furnaces' size and the important part it takes in industry, even though a small increase could take a big improvement on the thermal efficiency and energy saving effect of the whole system. According to the research result of J. C. Hellander, using high radiative infrared coating on the industrial furnace can improve the radiaitve heat transfer ability, which leads to the improvement of thermal efficiency. Generally speaking, the radiative rate of the regenerator (silica and aluminum martial) will decreased with the temperature increasing, however, the high radiative coating can make up this disadvantage.

In order to test the heat using condition and the thermal efficiency changing condition after using the high radiative coating on checker bricks, evaluate the thermal character, and reveal the application effect of the high radiative coating on Shandong Shiheng steel Co, Ltd. 1080 m³BF hot blast stoves, the heat diagnosis testing and analysis of the 1# and 3# stoves was carried out, which is good for the analysis of the energy saving effect and proposed measures for energy saving.

Detection Base of Thermal Diagnosis

Detection Cycle

Measured the complete heating cycle and the heat transfer cycle of 1# and 3# hot blast stove respectively, that is under the normal product condition of BF, measured the thermal condition between two combustion periods. Shandong Shiheng steel Co, Ltd. takes two stoves burning with another stove sending as the normal operation system, the burning time for 114 minutes, blowing time for 55 minutes, changing stove for 10 minutes, one cycle takes a total of 2 hours and 59 minutes.

The Base Temperature

Take the test-stage ambient temperature as a base temperature, this test make 10° as the base temperature.

Main Content of the Thermal Diagnosis

In this detection, the media flow and temperature is according to the average data of the inline meter records, gas component is analyzed by the flue gas analyzer on-site detection, the stoves' body heat dissipation and pipe heat dissipation used infrared thermometers. All instruments were debugged and adjusted before the test; the test results are true and reliable

Gas Parameters

(1) Gas Component Converter

The main fuel of the hot-blast stove is blast furnace gas, blast furnace gas composition analysis on-site frequently contain a small amount of oxygen, which is due to sampling and analysis, for this reason, of the blast furnace gas test results often mixed with 0.2%-0.4% oxygen, sometimes more than 0.6%. Actually, the composition of blast furnace gas should not be aerobic; you must deduct the oxygen and the corresponding nitrogen, and converted into 100%. As the blast furnace gas contain water after they wet—dust, which influence the gas heat value and theoretical combustion temperature. From this reason, we should select the wet gas component to calculate. In the thermal balance calculation, taking 5% water vapor of the amount of the gas (Be equal to 40 g/m³ gas).

In the calculation, the first test of gas components in the residual oxygen Z deduction into “dry ingredients” Z^(g), and then converted into “wet ingredients” Z^(s).

Form 1 Hot Blast Stove Burning Gas Component (%)

Dry gas component without Oxygen Z^(g) % Wet gas conversion component Z^(s) % CO CO₂ H₂ CH₄ N₂ CO CO₂ H₂ CH₄ N₂ H₂O 24.5 20.4 0.8 1.1 53.2 23.3 19.4 0.7 1.0 50.6 5.0 total 100.0 Total 100.0

(2) Fuel (Wet Gas) Low Heating Value

Fuel low heating value is calculated in accordance with 1% (volume)

Heat efficiency of the combustible component of wet gas, in this case, the combustible component is CO, H₂ and CH₄. The low heating value is 3378.49 KJ/m³.

Gas Parameters

Dry gas component is tested by the gas analyzer on-site, from the beginning of one testing cycle, take a sample records every 15 min, and make the average, then convert to the wet component according to the empirical formula.

Form 2 Gas Components in the Test Cycle (%)

Item O₂ CO₂ CO NO NO_(X) SO₂ C₃H₈ 1^(#) 1.85 25.82 0.0029 0.0008 0.0008 0.0003 0.0043 3^(#) 1.17 25.66 0.45 0.0008 0.0008 0 0.0059

Hot blast stove surface heat dissipation parameter.

Take the hot blast stove as seven segments for it has six platforms, every segment has eight measuring points. The testing results are shown in Form 3 and Form 4.

Form 3 1^(#) Hot Blast Stove Temperature (° C.)

North- North- South- South- East east North west West west South east Average 1-2 51.6 50.2 50.9 51.5 45.7 58.4 65.1 58.4 platforms 67.6 55.4 41.2 34 40.3 44.1 73.7 55.8 44 48.6 42.6 41.1 41.8 48.8 71.1 52.4 39.8 43.9 43.4 40.3 37.8 48.7 52.2 45.1 Average 50.75 49.52 44.52 41.72 41.4 50 65.52 52.92 49.54 2-3 62.4 76.8 68.6 66.4 61.9 70.5 76.2 77.9 platforms 79.6 64.5 57.2 52.4 75.9 78.2 74.1 60.8 65.9 46.4 48.5 67.8 68.4 74 Average 62.4 72.4 66.33 56.66 54.26 71.4 74.26 75.33 66.63 3-4 60.3 53.4 56.9 56 40.2 57 58.6 66 platforms 78.4 68.9 66 70.2 67.1 82.5 72.9 76.4 Average 69.35 61.15 61.45 63.1 53.65 69.75 65.75 71.2 64.42 4-5 51.2 39.5 53.1 54.7 42.7 57.1 52.4 51.3 50.25 platforms 5-6 25.3 20.5 19.3 18.5 16.5 32.4 39.1 31.4 platforms 41.2 36.1 37.9 38.4 23.7 41.6 44.4 38.5 Average 33.25 28.3 28.6 28.45 20.1 37 41.75 34.95 31.55 1 below 38.3 36.9 33.8 21.9 20.9 20.6 34 49.9 32.03 platform

Form 4 3^(#) Hot Blast Stove Temperature (° C.)

North- North- South- South- East east North west West west South east Average 1-2 56.6 65.2 71.6 63.8 54.8 66.7 63.7 55.6 platforms 50.8 58.4 76.1 61.7 44.1 52.7 59.8 61.1 51 63.4 74.9 61.3 43.2 53.9 51.9 56.8 45.8 51.8 58.3 48.2 40 53.6 60.1 55 average 51.05 59.7 70.2 58.75 45.52 56.72 58.87 57.12 57.24 2-3 75.7 86.5 70 81 66.2 77.2 86.9 80.2 platforms / 77 86.9 70.9 57.7 68.4 75.8 79.7 / 72.3 77 53.9 49.4 47.9 66.7 63.2 average 75.7 78.6 77.96 68.6 57.76 64.5 76.46 74.36 71.74 3-4 58.6 60.9 55 55.2 48.1 47.3 48.3 57 platforms 78.2 75.4 77.5 71.6 71.2 83 87.4 76.1 average 68.4 68.15 66.25 63.4 59.65 65.15 67.85 66.55 65.67 4-5 50.6 49.9 52.8 47.6 43.7 54.5 44.7 46 48.72 platforms 5-6 14.2 14.1 24 17.2 16.2 31.6 31.9 28.3 platforms 31.6 29.3 34 26.5 33.5 45.1 41.5 37.8 average 22.9 21.7 29 21.85 24.85 38.35 36.7 33.05 28.55 1 below 51.5 54.8 39.3 28.6 25.3 21.4 31.3 44 platform 46.7 46.4 38.7 28.6 25.3 21.4 21.2 42.5 average 49.1 50.6 39 28.6 25.3 21.4 26.25 43.25 35.43

Original Data of Thermal Diagnosis Test Form 5 1^(#) Stove Original Data

Hot blast Gas Combustion- Hot Stove pipe Gas Cool blast supporting air blast Flue gas superficial superficial Item Temp. flow Temp. Flow Temp. Flow Temp. Temp. temp. temp. unit ° C. m³/min ° C. m³/min ° C. m³/min ° C. ° C. m² m² data 40 1299 171 2509 183 622 1198 300 781 325

Form 6 3^(#) Stove Original Data

Hot blast Gas Combustion- Hot Flue Stove pipe Gas Cool blast supporting air blast gas Superficial superficial Item Temp. flow Temp. Flow Temp. flow Temp. Temp. Temp. temp. unit ° C. m³/min ° C. m³/min ° C. m³/min ° C. ° C. m² m² data 40 1299 171 2509 183 622 1173 313 781 325

Thermal Diagnosis Testing Results

The thermal diagnosis process is omitted; the results are shown in Form 7

Form 7 1^(#) Stove Thermal-Diagnosis Form

Heat receiving Heat consumption Symbol Item KJ/m³ % Symbol Item KJ/m³ % Q₁ Chemical heat of 1899.05 86.36 Q₁′ Heat hot air 1768.29 80.05 fuel taken away Q₂ Physical heat of 22.27 1.00 Q₂′ Physical 230.16 10.68 fuel heat fume taken away Q₃ Physical heat of 65.44 2.98 Q₃′ Chemical 2.62 0.12 combustion- incomplete supporting air combustion heat loss Q₄ Heat cool air 212.24 9.66 Q₄′ Gas 23.48 1.09 taken Mechanical water absorption heat Q₅′ Stove 72.33 3.36 surface heat dissipation capacity Q₆′ Hot air 58.31 2.71 pipe heat dissipation Capacity ΔQ Heat- 43.81 1.99 balance difference ΣQ 2199.00 100.00 ΣQ 2199.00 100.00

Form 8 3^(#) Hot Blast Stove Thermal-Diagnosis Form

Heat receiving Heat consumption Symbol Item KJ/m³ % Symbol Item KJ/m³ % Q₁ Chemical heat of 1899.05 86.55 Q₁′ Heat hot air 1665.57 74.93 fuel taken away Q₂ Physical heat of 22.27 1.00 Q₂′ Physical heat 274.49 13.22 fuel fume taken away Q₃ Physical heat of 61.97 2.83 Q₃′ Chemical 36.50 1.70 combustion- incomplete supporting air combustion heat loss Q₄ Heat cool air 212.24 9.62 Q₄′ Gas 24.03. 1.12 taken Mechanical water absorption heat Q₅′ Stove surface 86.60 4.04 heat dissipation capacity Q₆′ Hot air pipe 54.67 2.55 heat dissipation Capacity ΔQ Heat-balance 53.67 2.44 difference ΣQ 2199.00 100.00 ΣQ 2195.53 100.00

Result Analysis

Hot air temperature improved in large extent, exhausted gas temperature decreased.

Seen from the testing data and heat balance form, under the same condition with 3^(#) hot blast stove, the hot blast temperature of 1^(#) hot blast stove is 25° C. higher on average and exhausted gas temperature is 13° C. lower on average than 3^(#) hot blast stove. These two indicators cause the energy consumption is 3% lower and the heat taken away for temperature increasing increased 5.1% compared with 3^(#). The energy effect is obvious.

Gas Combustion Completely

Because of the increasing of checker bricks radiation of 1^(#), the heat storage ability is improved and the gas resistant time in the regenerator during the combustion period is prolonged. Seen from the analysis, CO content in gas of 1^(#) hot blast stove is much more lower than 3^(#) hot blast stove, which reduced the heat consumption for chemical incomplete combustion to 0.12% from 1.7%. Heat utilization is more perfect.

Thermal Efficiency Increasing

{circle around (1)} Thermal efficiency of the body of hot stove η₁

${1^{\#}\text{:}\mspace{14mu} \eta_{1}} = {\frac{Q_{1}^{\prime} - Q_{4} + Q_{6}^{\prime}}{{\sum\; Q} - Q_{4}} = {\frac{1768.29 - 212.24 + 58.31}{2199.00 - 212.24}81.26\%}}$ ${3^{\#}\text{:}\mspace{14mu} \eta_{1}} = {\frac{Q_{1}^{\prime} - Q_{4} + Q_{6}^{\prime}}{{\sum\; Q} - Q_{4}} = {\frac{1665.57 - 212.24 + 54.67}{2195.53 - 212.24}76.03\%}}$

{circle around (2)} Thermal efficiency of the hot stove η₂

${1^{\#}\text{:}\mspace{14mu} \eta_{2}} = {{\frac{Q_{1}^{\prime} - Q_{4}}{{\sum\; Q} - Q_{4}} \times 100} = {\frac{1768.29 - 212.24}{2199.00 - 212.24}78.32\%}}$ ${3^{\#}\text{:}\mspace{14mu} \eta_{2}} = {{\frac{Q_{1}^{\prime} - Q_{4}}{{\sum\; Q} - Q_{4}} \times 100} = {\frac{1665.57 - 212.24}{2195.53 - 212.24}73.28\%}}$

Conclusion:

The blast temperature of the hot blast stove (without coating) is 25° C. higher on average than the one without coating, the gas temperature is reduced by 13° C., and the energy consumption reduced by 3%.

The gas combustion of the hot blast stove (with coating) is complete, and the combustible component in gas is decreased to a large extent. Heat loss decreased from 1.7% to 0.12%.

The thermal efficiency of the hot blast stove (with coating) is improved by 5% than the one without coating, the energy saving effect is obvious and stable.

Commercial Success

The heat retainers for the hot blast stoves of the blast furnaces of the present invention have been used in commerce in at least 217 blast furnace hot stoves and 3 coke batteries by more than 50 iron and steel companies, and they are commercially successful.

The heat storage ability of the heat retainer with a high radiative coating of the invention is higher by at least about 15% at under 1300° C. compared with that described in the prior art. The hot blast temperature is increased by at least 15° C., the exhaust gas temperature is reduced by at least 13° C., and gas consumption is decreased by at least 7%. In addition, the reduction of CO₂ emission is successfully realized.

This invention is not to be limited to the specific embodiments disclosed herein and modifications for various applications and other embodiments are intended to be included within the scope of the appended claims. While this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and following claims.

All publications and patent applications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application mentioned in this specification.

Emissivity of Common Metal and Non-Metal Materials

Metal Material Temp ° F. (° C.) Emissivity Alloys 20-Ni, 24-CR, 55-FE, Oxidized 392 (200) 0.9 20-Ni, 24-CR, 55-FE, Oxidized 932 (500) 0.97 60-Ni, 12-CR, 28-FE, Oxidized 518 (270) 0.89 60-Ni, 12-CR, 28-FE, Oxidized 1040 (560) 0.82 80-Ni, 20-CR, Oxidized 212 (100) 0.87 80-Ni, 20-CR, Oxidized 1112 (600) 0.87 80-Ni, 20-CR, Oxidized 2372 (1300) 0.89 Aluminum Unoxidized 77 (25) 0.02 Unoxidized 212 (100) 0.03 Unoxidized 932 (500) 0.06 Oxidized 390 (199) 0.11 Oxidized 1110 (599) 0.19 Oxidized at 599° C. (1110° F.) 390 (199) 0.11 Oxidized at 599° C. (1110° F.) 1110 (599) 0.19 Heavily Oxidized 200 (93) 0.2 Heavily Oxidized 940 (504) 0.31 Highly Polished 212 (100) 0.09 Roughly Polished 212 (100) 0.18 Commercial Sheet 212 (100) 0.09 Highly Polished Plate 440 (227) 0.04 Highly Polished Plate 1070 (577) 0.06 Bright Rolled Plate 338 (170) 0.04 Bright Rolled Plate 932 (500) 0.05 Alloy A3003, Oxidized 600 (316) 0.4 Alloy A3003, Oxidized 900 (482) 0.4 Alloy 1100-0 200-800 (93-427) 0.05 Alloy 24ST 75 (24) 0.09 Alloy 24ST, Polished 75 (24) 0.09 Alloy 75ST 75 (24) 0.11 Alloy 75ST, Polished 75 (24) 0.08 Bismuth, Bright 176 (80) 0.34 Bismuth, Unoxidized 77 (25) 0.05 Bismuth, Unoxidized 212 (100) 0.06 Brass 73% Cu, 27% Zn, Polished 476 (247) 0.03 73% Cu, 27% Zn, Polished 674 (357) 0.03 62% Cu, 37% Zn, Polished 494 (257) 0.03 62% Cu, 37% Zn, Polished 710 (377) 0.04 83% Cu, 17% Zn, Polished 530 (277) 0.03 Matte 68 (20) 0.07 Burnished to Brown Color 68 (20) 0.4 Cu—Zn, Brass Oxidized 392 (200) 0.61 Cu—Zn, Brass Oxidized 752 (400) 0.6 Cu—Zn, Brass Oxidized 1112 (600) 0.61 Unoxidized 77 (25) 0.04 Unoxidized 212 (100) 0.04 Cadmium 77 (25) 0.02 Carbon Lampblack 77 (25) 0.95 Unoxidized 77 (25) 0.81 Unoxidized 212 (100) 0.81 Unoxidized 932 (500) 0.79 Candle Soot 250 (121) 0.95 Filament 500 (260) 0.95 Graphitized 212 (100) 0.76 Graphitized 572 (300) 0.75 Graphitized 932 (500) 0.71 Chromium 100 (38) 0.08 Chromium 1000 (538) 0.26 Chromium, Polished 302 (150) 0.06 Cobalt, Unoxidized 932 (500) 0.13 Cobalt, Unoxidized 1832 (1000) 0.23 Columbium, Unoxidized 1500 (816) 0.19 Columbium, Unoxidized 2000 (1093) 0.24 Copper Cuprous Oxide 100 (38) 0.87 Cuprous Oxide 500 (260) 0.83 Cuprous Oxide 1000 (538) 0.77 Black, Oxidized 100 (38) 0.78 Etched 100 (38) 0.09 Matte 100 (38) 0.22 Roughly Polished 100 (38) 0.07 Polished 100 (38) 0.03 Highly Polished 100 (38) 0.02 Rolled 100 (38) 0.64 Rough 100 (38) 0.74 Molten 1000 (538) 0.15 Molten 1970 (1077) 0.16 Molten 2230 (1221) 0.13 Nickel Plated 100-500 (38-260) 0.37 Dow Metal 0.4-600 (−18-316) 0.15 Gold Enamel 212 (100) 0.37 Plate (.0001) Plate on .0005 Silver 200-750 (93-399) .11-.14 Plate on .0005 Nickel 200-750 (93-399) .07-.09 Polished 100-500 (38-260) 0.02 Polished 1000-2000 (5381093) 0.03 Haynes Alloy C Oxidized 600-2000 (316-1093) .90-.96 Haynes Alloy 25, Oxidized 600-2000 (316-1093) .86-.89 Haynes Alloy X Oxidized 600-2000 (316-1093) .85-.88 Inconel Sheet 1000 (538) 0.28 Inconel Sheet 1200 (649) 0.42 Inconel Sheet 1400 (760) 0.58 Inconel X, Polished 75 (24) 0.19 Inconel B, Polished 75 (24) 0.21 Iron Oxidized 212 (100) 0.74 Oxidized 930 (499) 0.84 Oxidized 2190 (1199) 0.89 Unoxidized 212 (100) 0.05 Red Rust 77 (25) 0.7 Rusted 77 (25) 0.65 Liquid 2760-3220 (1516-1771) .42-.45 Cast Iron Oxidized 390 (199) 0.64 Oxidized 1110 (599) 0.78 Unoxidized 212 (100) 0.21 Strong Oxidation 40 (104) 0.95 Strong Oxidation 482 (250) 0.95 Liquid 2795 (1535) 0.29 Wrought Iron Dull 77 (25) 0.94 Dull 660 (349) 0.94 Smooth 100 (38) 0.35 Polished 100 (38) 0.28 Lead Polished 100-500 (38-260) .06-.08 Rough 100 (38) 0.43 Oxidized 100 (38) 0.43 Oxidized at 1100 100 (38) 0.63 Gray Oxidized 100 (38) 0.28 Magnesium 100-500 (38-260) .07-.13 Magnesium Oxide 1880-3140 (1027-1727) .16-.20 Mercury 32 (0) 0.09 Mercury 77 (25) 0.1 Mercury 100 (38) 0.1 Mercury 212 (100) 0.12 Monel, Ni—Cu 392 (200) 0.41 Monel, Ni—Cu 752 (400) 0.44 Monel, Ni—Cu 1112 (600) 0.46 Monel, Ni—Cu Oxidized 68 (20) 0.43 Monel, Ni—Cu Oxidized 1110 (599) 0.46 at 1110° F. Nickel Polished 100 (38) 0.05 Oxidized 100-500 (38-260) .31-.46 Unoxidized 77 (25) 0.05 Unoxidized 212 (100) 0.06 Unoxidized 932 (500) 0.12 Unoxidized 1832 (1000) 0.19 Electrolytic 100 (38) 0.04 Electrolytic 500 (260) 0.06 Electrolytic 1000 (538) 0.1 Electrolytic 2000 (1093) 0.16 Nickel Oxide 1000-2000 (538-1093) .59-.86 Palladium Plate 200-750 (93-399) .16-.17 (.00005 on .0005 silver) Platinum 100 (38) 0.05 Platinum 500 (260) 0.05 Platinum 1000 (538) 0.1 Platinum, Black 100 (38) 0.93 Platinum, Black 500 (260) 0.96 Platinum, Black 2000 (1093) 0.97 Platinum Oxidized at 1100 500 (260) 0.07 Platinum Oxidized at 1100 1000 (538) 0.11 Rhodium Flash 200-700 (93-371) .10-.18 (0.0002 on 0.0005 Ni) Silver Plate (0.0005 on Ni) 200-700 (93-371) .06-.07 Polished 100 (38) 0.01 Polished 500 (260) 0.02 Polished 1000 (538) 0.03 Polished 2000 (1093) 0.03 Steel Cold Rolled 200 (93) .75-.85 Ground Sheet 1720-2010 (938-1099) .55-.61 Polished Sheet 100 (38) 0.07 Polished Sheet 500 (260) 0.1 Polished Sheet 1000 (538) 0.14 Mild Steel, Polished 75 (24) 0.1 Mild Steel, Smooth 75 (24) 0.12 Mild Steel, liquid 2910-3270 (1599-1793) 0.28 Steel, Unoxidized 212 (100) 0.08 Steel, Oxidized 77 (25) 0.8 Steel Alloys Type 301, Polished 75 (24) 0.27 Type 301, Polished 450 (232) 0.57 Type 301, Polished 1740 (949) 0.55 Type 303, Oxidized 600-2000 (316-1093) .74-.87 Type 310, Rolled 1500-2100 (8161149) .56-.81 Type 316, Polished 75 (24) 0.28 Type 316, Polished 450 (232) 0.57 Type 316, Polished 1740 (949) 0.66 Type 321 200-800 (93-427) .27-.32 Type 321 Polished 300-1500 (149-815) .18-.49 Type 321 w/BK Oxide 200-800 (93-427) .66-.76 Type 347, Oxidized 600-2000 (316-1093) .87-.91 Type 350 200-800 (93-427) .18-.27 Type 350 Polished 300-1800 (149-982) .11-.35 Type 446, Polished 300-1500 (149-815) .15-.37 Type 17-7 PH 200-600 (93-316) .44-.51 Type 17-7 PH Polished 300-1500 (149-815) .09-.16 Type C1020, Oxidized 600-2000 (316-1093) .87-.91 Type PH-15-7 MO 300-1200 (149-649) .07-.19 Stellite, Polished 68 (20) 0.18 Tantalum, Unoxidized 1340 (727) 0.14 Tantalum, Unoxidized 2000 (1093) 0.19 Tantalum, Unoxidized 3600 (1982) 0.26 Tantalum, Unoxidized 5306 (2930) 0.3 Tin, Unoxidized 77 (25) 0.04 Tin, Unoxidized 212 (100) 0.05 Tinned Iron, Bright 76 (24) 0.05 Tinned Iron, Bright 212 (100) 0.08 Titanium Alloy C110M, Polished 300-1200 (149-649) .08-.19 Oxidized at 538° C. (1000° F.) 200-800 (93-427) .51-.61 Alloy Ti-95A, Oxidized 200-800 (93-427) .35-.48 at 538° C. (1000° F.) Anodized onto SS 200-600 (93-316) .96-.82 Tungsten Unoxidized 77 (25) 0.02 Unoxidized 212 (100) 0.03 Unoxidized 932 (500) 0.07 Unoxidized 1832 (1000) 0.15 Unoxidized 2732 (1500) 0.23 Unoxidized 3632 (2000) 0.28 Filament (Aged) 100 (38) 0.03 Filament (Aged) 1000 (538) 0.11 Filament (Aged) 5000 (2760) 0.35 Uranium Oxide 1880 (1027) 0.79 Zinc Bright, Galvanized 100 (38) 0.23 Commercial 99.1% 500 (260) 0.05 Galvanized 100 (38) 0.28 Oxidized 500-1000 (260-538) 0.11 Polished 100 (38) 0.02 Polished 500 (260) 0.03 Polished 1000 (538) 0.04 Polished 2000 (1093) 0.06 Non-Metals Material Temp ° F. (° C.) Emissivity Adobe 68 (20) 0.9 Asbestos Board 100 (38) 0.96 Cement 32-392 (0-200) 0.96 Cement, Red 2500 (1371) 0.67 Cement, White 2500 (1371) 0.65 Cloth 199 (93) 0.9 Paper 100-700 (38-371) 0.93 Slate 68 (20) 0.97 Asphalt, pavement 100 (38) 0.93 Asphalt, tar paper 68 (20) 0.93 Basalt 68 (20) 0.72 Brick Red, rough 70 (21) 0.93 Gault Cream 2500-5000 (1371-2760) .26-.30 Fire Clay 2500 (1371) 0.75 Light Buff 1000 (538) 0.8 Lime Clay 2500 (1371) 0.43 Fire Brick 1832 (1000) .75-.80 Magnesite, Refractory 1832 (1000) 0.38 Grey Brick 2012 (1100) 0.75 Silica, Glazed 2000 (1093) 0.88 Silica, Unglazed 2000 (1093) 0.8 Sandlime 2500-5000 (1371-2760) .59-.63 Carborundum 1850 (1010) 0.92 Ceramic Alumina on Inconel 800-2000 (427-1093) .69-.45 Earthenware, Glazed 70 (21) 0.9 Earthenware, Matte 70 (21) 0.93 Greens No. 5210-2C 200-750 (93-399) .89-.82 Coating No. C20A 200-750 (93-399) .73-.67 Porcelain 72 (22) 0.92 White Al₂O₃ 200 (93) 0.9 Zirconia on Inconel 800-2000 (427-1093) .62-.45 Clay 68 (20) 0.39 Fired 158 (70) 0.91 Shale 68 (20) 0.69 Tiles, Light Red 2500-5000 (1371-2760) .32-.34 Tiles, Red 2500-5000 (1371-2760) .40-.51 Tiles, Dark Purple 2500-5000 (1371-2760) 0.78 Concrete Rough 32-2000 (0-1093) 0.94 Tiles, Natural 2500-5000 (1371-2760) .63-.62 Brown 2500-5000 (1371-2760) .87-.83 Black 2500-5000 (1371-2760) .94-.91 Cotton Cloth 68 (20) 0.77 Dolomite Lime 68 (20) 0.41 Emery Corundum 176 (80) 0.86 Glass Convex D 212 (100) 0.8 Convex D 600 (316) 0.8 Convex D 932 (500) 0.76 Nonex 212 (100) 0.82 Nonex 600 (316) 0.82 Nonex 932 (500) 0.78 Smooth 32-200 (0-93) .92-.94 Granite 70 (21) 0.45 Gravel 100 (38) 0.28 Gypsum 68 (20) .80-.90 Ice, Smooth 32 (0) 0.97 Ice, Rough 32 (0) 0.98 Lacquer Black 200 (93) 0.96 Blue, on Al Foil 100 (38) 0.78 Clear, on Al Foil (2 coats) 200 (93) .08-.09 Clear, on Bright Cu 200 (93) 0.66 Clear, on Tarnished Cu 200 (93) 0.64 Red, on Al Foil (2 coats) 100 (38) .60-.74 White 200 (93) 0.95 White, on Al Foil (2 coats) 100 (38) .69-.88 Yellow, on Al Foil (2 coats) 100 (38) .57-.79 Lime Mortar 100-500 (38-260) .90-.92 Limestone 100 (38) 0.95 Marble, White 100 (38) 0.95 Smooth, White 100 (38) 0.56 Polished Grey 100 (38) 0.75 Mica 100 (38) 0.75 Oil on Nickel 0.001 Film 72 (22) 0.27 0.002″ 72 (22) 0.46 0.005″ 72 (22) 0.72 Thick″ 72 (22) 0.82 Oil, Linseed On Al Foil, uncoated 250 (121) 0.09 On Al Foil, 1 coat 250 (121) 0.56 On Al Foil, 2 coats 250 (121) 0.51 On Polished Iron, .001 Film 100 (38) 0.22 On Polished Iron, .002 Film 100 (38) 0.45 On Polished Iron, .004 Film 100 (38) 0.65 On Polished Iron, Thick Film 100 (38) 0.83 Paints Blue, Cu₂O₃ 75 (24) 0.94 Black, CuO 75 (24) 0.96 Green, Cu₂O₃ 75 (24) 0.92 Red, Fe₂O₃ 75 (24) 0.91 White, Al₂O₃ 75 (24) 0.94 White, Y₂O₃ 75 (24) 0.9 White, ZnO 75 (24) 0.95 White, MgCO₃ 75 (24) 0.91 White, ZrO₂ 75 (24) 0.95 White, ThO₂ 75 (24) 0.9 White, MgO 75 (24) 0.91 White, PbCO3 75 (24) 0.93 Yellow, PbO 75 (24) 0.9 Yellow, PbCrO₄ 75 (24) 0.93 Paints, Aluminum 100 (38) .27-.67 10% Al 100 (38) 0.52 26% Al 100 (38) 0.3 Dow XP-310 200 (93) 0.22 Paints, Bronze Low .34-.80 Gum Varnish (2 coats) 70 (21) 0.53 Gum Varnish (3 coats) 70 (21) 0.5 Cellulose Binder (2 coats) 70 (21) 0.34 Paints, Oil All colors 200 (93) .92-.96 Black 200 (93) 0.92 Black Gloss 70 (21) 0.9 Camouflage Green 125 (52) 0.85 Flat Black 80 (27) 0.88 Flat White 80 (27) 0.91 Grey-Green 70 (21) 0.95 Green 200 (93) 0.95 Lamp Black 209 (98) 0.96 Red 200 (93) 0.95 White 200 (93) 0.94 Red Lead 212 (100) 0.93 Rubber, Hard 74 (23) 0.94 Rubber, Soft, Grey 76 (24) 0.86 Sand 68 (20) 0.76 Sandstone 100 (38) 0.67 Sandstone, Red 100 (38) .60-.83 Sawdust 68 (20) 0.75 Shale 68 (20) 0.69 Silica, Glazed 1832 (1000) 0.85 Silica, Unglazed 2012 (1100) 0.75 Silicon Carbide 300-1200 (149-649) .83-.96 Silk Cloth 68 (20) 0.78 Slate 100 (38) .67-.80 Snow, Fine Particles 20 (−7) 0.82 Snow, Granular 18 (−8) 0.89 Soil Surface 100 (38) 0.38 Black Loam 68 (20) 0.66 Plowed Field 68 (20) 0.38 Soot Acetylene 75 (24) 0.97 Camphor 75 (24) 0.94 Candle 250 (121) 0.95 Coal 68 (20) 0.95 Stonework 100 (38) 0.93 Water 100 (38) 0.67 Wood Low .80-.90 Beech Planed 158 (70) 0.94 Oak, Planed 100 (38) 0.91 Spruce, Sanded 100 (38) 0.89 

1. A heat retainer for a hot blast stove of a blast furnace, the heat retainer adapted to function at temperatures of about 1200° C. present during operation of a hot blast stove of a blast furnace, and adapted to absorb thermal energy from air in the hot blast stove of the blast furnace, the heat retainer experiencing a heat storage period and a heat release period, the heat retainer having a coating layer, wherein: at least one surface of said heat retainer is coated with a high radiative material forming said coating layer; the thickness of said coating layer is critically between 0.02 mm and 3 mm; the heat retainer absorbs energy in the heat storage period, whereby end temperature of the heat retainer is increased during heat storage period compared to what it would have been in the absence of said coating layer; the heat retainer emits energy in the heat release period, whereby end temperature of the heat retainer is decreased during heat release period compared to what it would have been in the absence of said coating layer; the heat retainer absorbs energy or emits energy mainly by radiation at a wavelength of between 1 and 5 μm.
 2. The heat retainer of claim 1, wherein said coating layer achieves rapid and efficient heat transfer and increases the heat storage capacity of the heat retainer.
 3. The heat retainer of claim 1, wherein said high radiative material is not highly-reflective.
 4. The heat retainer of claim 1, adapted to transfer more heat by radiation than by convection.
 5. The heat retainer of claim 1, adapted to absorb and emit heat non-simultaneously, wherein a steady-state for heat absorption and emission is not reached during a heat absorption period or a heat emission period.
 6. The heat retainer of claim 1, comprising a core and a coating layer, wherein the heat emissivity of the coating layer is greater than the heat emissivity of the core.
 7. The heat retainer of claim 6, wherein said coating layer increases heat absorption and heat radiation ability of the core.
 8. The heat retainer of claim 6, further comprising at least one cavity in said core.
 9. The heat retainer of claim 8, wherein said cavity passes through the matrix from its one end to another and said coating layer completely coats the surface of said cavity.
 10. The heat retainer of claim 1, wherein the substrate of the heat retainer is made of one of a refractory material, or a ceramic material.
 11. The heat retainer of claim 1, wherein said coating layer comprises one or more of the following: Cr₂O₃, clay, montmorillonite, brown corundum, silicon carbide, TiO₂, Al₂O₃, aluminum hydroxide, zirconium oxide, phosphoric acid, or hydrated sodium silicate gel.
 12. A heat retainer comprising: a core having a first heat emissivity; a plurality of inner passages in said core, said plurality of said inner passages extending from a first surface of said core to a second surface of said core, and being immovable with respect to one another; and a coating layer coating said core and said passages, said coating layer having a second heat emissivity; wherein said coating layer comprises a high radiative material; the thickness of said coating layer is critically between 0.02 mm and 3 mm; said second heat emissivity is greater than said first heat emissivity; said coating layer achieves rapid and efficient heat transfer and increases the heat storage capacity of the heat retainer; said high radiative material is not highly-reflective; said heat retainer is adapted to absorb heat from and to emit heat to air in a hot blast stove of a blast furnace mainly by thermal radiation; said heat retainer is adapted to absorb and emit heat non-simultaneously; said heat retainer is adapted for use in a high temperature heat exchanger and for use at temperatures below 1400° C. present during operation of a hot blast stove of a blast furnace; the heat retainer experiences a heat storage period and a heat release period; the heat retainer absorbs energy in the heat storage period, whereby end temperature of the heat retainer is increased during heat storage period relative to what it would have been without said coating layer; the heat retainer emits energy in the heat release period, whereby end temperature of the heat retainer is decreased during heat release period relative to what it would have been without said coating layer; and energy of thermal radiation is mainly at a wavelength of between 1 and 5 μm.
 13. The heat retainer of claim 1, wherein said coating layer achieves rapid and efficient heat transfer and increases the heat storage capacity of the heat retainer.
 14. The heat retainer of claim 1, wherein said high radiative material is not highly-reflective.
 15. The heat retainer of claim 1, adapted to transfer more heat by radiation than by convection.
 16. The heat retainer of claim 1, adapted to absorb and emit heat non-simultaneously.
 17. The heat retainer of claim 1, comprising a core and a coating layer, wherein the heat emissivity of the coating layer is greater than the heat emissivity of the core.
 18. The heat retainer of claim 6, wherein said coating layer increases heat absorption and heat radiation ability of the core.
 19. The heat retainer of claim 6, further comprising at least one cavity in said core.
 20. The heat retainer of claim 8, wherein said cavity passes through the matrix from its one end to another and said coating layer completely coats the surface of said cavity.
 21. A method for enhancing radiative heat absorption and radiative heat emission and for simultaneously reducing heat reflection in a heat retainer for a hot blast stove of a blast furnace, comprising: placing into a hot blast stove of a blast furnace a core coated with a coating layer, and operating said hot blast stove or said blast furnace at usual operating temperatures about 1200° C.; wherein said core has a first heat emissivity; said coating layer has a second heat emissivity; said second heat emissivity is greater than said first heat emissivity; said coating layer comprises a high radiative material; the thickness of said coating layer is critically between 0.02 mm and 3 mm; said coating layer achieves rapid and efficient heat transfer and increases the heat storage capacity of the heat retainer; said high radiative material is not highly-reflective; said heat retainer absorbs heat from and emits heat to air in a hot blast stove of a blast furnace mainly by thermal radiation; said heat retainer absorbs and emits heat non-simultaneously; the heat retainer experiences a heat storage period and a heat release period; the heat retainer absorbs energy in the heat storage period, whereby end temperature of the heat retainer is increased during heat storage period; the heat retainer emits energy in the heat release period, whereby end temperature of the heat retainer is decreased during heat storage period; and energy of thermal radiation is mainly in a wavelength of 1-5 μm. 